There are in existence various hair styling apparatus such as hair curlers. In a conventional hair curler, tresses of hair are wound around a heating barrel. A user may then press a button to pass electricity to the heating barrel to heat up the barrel, so as to curl the hair by heating. In order to curl the hair, the heating barrel has to be heated up to a very high temperature. It is well known that it is dangerous to operate such an apparatus, whether to the user or to the one whose hair is being styled.